## isotope

Set the isotope of the nucleus.

**Input block**

**Extended variant**

`isotope:`

`[element-symbol]: [integer]`

`[element-index]: [integer]`

`...`

**Default**

`Isotopes with largest abundance and non-zero spin.`

**Example**

```
isotope:
N : 15
10 : 2
```

### Note

- The data in the isotope block is processed line by line, therefore the latter data overwrites the former one.

- Isotope block is processed before g-factor and mass block, therefore the data can be overwritten by these blocks.

## g-factor

Specify the nuclear g-factor.

**Input block**

**Extended variant**

`g-factor:`

`[element-symbol]: [integer]`

`[element-index]: [integer]`

`...`

**Default**

`G-factor of isotopes with largest abundance and non-zero spin.`

**Example**

```
g-factor:
H : 5.5856947
2 : 0.8574382
C : 1.4048236
```

### Note

- The data in the g-factor block is processed line by line, therefore the latter data overwrites the former one.

- Data from g-factor block overwrites setting from the isotope block.

### Tip

- Spin-spin coupling tensor is calculated only for NMR active atoms (non-zero g-factor). This keyword can be used to set non-zero g-factor for elements witch isotopes have only zero or unknown magnetic moment to perform hypothetical studies (like f.e. At).

## mass

Set the mass of the nucleus.

**Input block**

**Extended variant**

`mass:`

`[element-symbol]: [integer]`

`[element-index]: [integer]`

`...`

**Default**

`Mass of isotopes with largest abundance and non-zero spin.`

**Example**

```
mass:
N : 14.0030740048
10 : 15.0001088982
```

### Note

- The data in the mass block is processed line by line, therefore the latter data overwrites the former one.

- Data from mass block overwrites setting from the isotope block.

## dft-kernel

Set details of the DFT kernel.

**Input block**

**Short variant**

```
dft-kernel:
[functional]
```

**Extended variant**

`dft-kernel:`

`functional: [functional]`

`type: [formatted-string]`

`skip: [Boolean]`

**Default**

```
dft-kernel:
functional : from-scf
type : analytical
skip : False
```

**Example**

```
dft-kernel:
functional : ALDA
type : analytical
```

### Warning

- The use of skip, ALDA and XLADA options is not recommended, since they approximate the full DFT kernel. Their use is only recommended when comparing the calculated data to the implementation in other QCh codes, where these approximations can not be avoided.

## eri

Specify details associated with the evaluation of electron repulsion integrals (ERI) and related two-electron Fock contributions.

**Input block**

**Extended variant**

`eri:`

`class: [string]`

`threshold: [real]`

**Default**

`Default is taken from the scf step of the calculation.`

**Example**

```
eri:
class: ssss/abcd
threshold: 1.e-15
```

### Note

- Keyword acceleration is taken from the scf procedure and is not allowed to change it for the calculation of the sscc.

## analysis

Analyze contributions from molecular orbitals to the paramagnetic part of the NMR shielding tensor.

**Input block**

**Short variant**

```
analysis:
[analyze]
```

**Extended variant**

`analysis:`

`analyze: [analyze]`

`xyz-values: [string]`

`sort: [Boolean]`

`occ-threshold: [real]`

`vir-threshold: [real]`

`energy-degeneracy: [real]`

`output-digits: [integer]`

**Default**

```
analysis:
analyze : none
xyz-values : principal
sort : True
occ-threshold : 0.1
vir-threshold : 0.1
energy-degeneracy : 1.0e-8
output-digits : 2
```

**Example**

```
analysis:
analyze : MO
xyz-values : diagonal
sort : False
occ-threshold : 0.01
vir-threshold : 0.01
```

## grid

Specify atomic grids for the numerical evaluation of exchange-correlation DFT contributions.

**Input block**

**Short variant**

```
grid:
[grid-type]
```

**Extended variant**

`grid:`

`all: [string]`

`[element-symbol]: [string]`

`[element-index]: [string]`

`...`

**Default**

`Grid is taken from scf part of the calculation.`

**Example**

`grid: large`

```
grid:
C: medium
7: large
```

### Note

- There can be multiple instances of element-symbol and element-index in the grid block.

- While lines in the grid block can be mixed, they are always processed in the following order: "all", all "element-symbol" and all "element-index" keywords.

- The order of processing the data matters, since the latter lines rewrite the data of the former lines. This way one can easily set the same grid for all Carbons except the Carbon number 7 (see example).

## reference-atom

Specify the geometry index of the reference atom for the sscc calculation.

**Input line****Default**

```
reference-atom:
[integer]
```

`none`

**Example**

`reference-atom: 2`

## active-atoms

Specify atoms for the calculation of NMR shielding tensor.

**Input line****Default**

```
active-atoms:
[formatted-string]
```

`active-atoms: all`

**Example**

`active-atoms: H`

`active-atoms: 5, C, 1-3`

## convergence

Convergence threshold for the self-consistent procedure.

**Input line****Default**

```
convergence:
[real]
```

`convergence: 1.0e-5`

**Example**

`convergence: 1.0e-3`

## dmixing

Mixing parameter for the self-consistent procedure.

**Input line****Default**

```
dmixing:
[real]
```

`dmixing: 1.0e0`

**Example**

`dmixing: 0.2e0`

## maxiterations

Maximum number of iterations for the self-consistent procedure.

**Input line****Default**

```
maxiterations:
[integer]
```

`maxiterations: 30`

**Example**

`maxiterations: 20`

## nuclear-spin

Orientation of the nuclear spin perturbation.

## response-only

It allows to calculate only response molecular orbitals.

**Input line****Default**

```
response-only:
[Boolean]
```

`response-only: False`

**Example**

`response-only: True`

### Tip

- Combine keywords response-only and nuclear-spin to speed up calculation, if you are (f.e.) interested only in the visualization of certain component of magnetically induced spin density.

## Latest Publications

### JCP just accepted two our theoretical articles on "Four-component relativistic eigenvalue- and damped-response TDDFT theory on excitations energies, electronic absorption, and natural circular dischroism using a stable noncollinear DFT ansatz"

## Useful Links

## Our Contacts

Department of Chemistry

UiT The Arctic University of Norway

Tromsø, NO-9037 Norway

Email: info@respectprogram.eu